Patricia Yolanda Santos-Vera, Mauro Geovany Campo-Yanez, Dina Johanna Erazo-Loor, Kahya Belen Oña-Suquillot, Sandra Elizabeth Mejia-Villacres
The schooling of students with diverse needs often depends on reactive curricular adaptations; this article reviews the evidence on “in-classroom” school placements (co-teaching, push-in supports, flexible splitting) planned with UDL to reduce barriers from the outset. An exploratory literature review was conducted using systematic procedures: searches in Scopus, Web of Science, and ERIC up to January 6, 2026, inclusion criteria for early childhood, primary, and secondary education, PRISMA-type screening with double review, and narrative synthesis with subgroup analysis. The findings show generally moderate performance improvements with UDL instruction (meta-analysis g≈0.43; greater in small groups) and moderate effects of co-teaching on achievement (g≈0.47), along with more robust gains in participation and accessibility. Feasibility depends on teacher training, co-planning time, and fidelity monitoring (e.g., UDL-OMT), and the future agenda calls for more rigorous studies and cost-effectiveness analyses in basic education.